#include<iostream>
#include<set>
using namespace std;

int main()
{
	set<long long>s;
	long long n;
	cin >> n;
	long long x;
	for (int i = 1; i < n; i++)
	{
		cin >> x;
		s.insert(x);
	}
	long long firt = *s.begin();
	for (set<long long>::iterator it = ++s.begin(); it != s.end(); it++)
	{
		if (*it - firt != 1)
		{
			cout << firt + 1 << endl;
			return 0;
		}
		firt = *it;
	}
	if (*s.begin() == 1)
		cout << n << endl;
	else
		cout << "1" << endl;
}